Jose Da Silva wrote: > Now imagine you are watching the news and they show an on-the-spot > segment recorded from a handy-cam type camera. I would think that you > are getting colourburst according to the portable camera and not > according to studio-quality colourburst. It doesn't work that way. If you think about it, it can't because if each camera had independently running sync and color burst, the picture would jump every time it was switched. A television station will have a master sync and color burst generator. Anything that can't sync to that directly, and perhaps everything anyway goes thru a timebase corrector. It used to be that TV stations would get a very accurate sync and color burst feed from whatever network they were affiliated with, and these networks had expensive sync generators that were regularly compared to the NBS atomic clock. The color burst deviations from the official standard were even published. This was some years ago before things were all digital, and NBS is now NIST. I don't know how/if things are done differently now. But aren't we losing sight of what Jinx wants to do? I thought he wanted to plunk some existing crystal on a PIC, then calibrate to the specific crystal during manufacturing. No matter how accurate the calibration is when it's done, the crystal will age and there will be deviations due to temperature changes. I doubt he could specify the units to be better than 20ppm even if they were calibrated to 0ppm error at manufacturing time. This means that about 5ppm for the reference is good enough, and going beyond that won't allow a tighter spec on the product anyway. So, the question is how to come up with an accurate (5ppm or so) reference to calibrate the individual crystals to. I think he's already seen that the power line isn't good enough at any one point in time. I can think of several choices: 1 - Buy a frequency reference. These are commercially available to better than 5ppm using calibrated crystals that have been aged and are actively temperature controlled. HP used to make a portable cesium standard for only a few 1000 $, but that sounds like rather overkill. 2 - Pick up your local radio time standard transmission. New Zealand isn't that big, so I'm assuming a suitably low frequency signal from a local transmitter can be picked up reliably anywhere in the country. This should work fine as long as you can get the ground wave, which you probably can since you'd be close enough. I'm 2000 miles from WWVB in Boulder Colorado, and couldn't use it's signal for that purpose here but Jinx probably has much better reception from the NZ transmitter. 3 - Use a GPS that puts out a time signal. GPS is based on very accurate time measurments and is driven by atomic clocks way more accurate than needed. There are GPS units that tap into this and export highly accurate and traceable time signals. ****************************************************************** Embed Inc, Littleton Massachusetts, (978) 742-9014. #1 PIC consultant in 2004 program year. http://www.embedinc.com/products -- http://www.piclist.com PIC/SX FAQ & list archive View/change your membership options at http://mailman.mit.edu/mailman/listinfo/piclist